Abstract A series of polyurethaneurea (PUU) aqueous dispersions
either with diethyltoluenediamine (DETDA) or ethylenediamine (EDA) as
chain extender were prepared with polyester polyol, isophorone
disocyanate and dimethylol propionic acid (DMPA), and characterized. It
was found that the physical properties of the PUU aqueous dispersions
prepared with DETDA were similar to or better than those prepared with
EDA. Compared with the EDA- extended waterborne PUU films, the water
resistance and the mechanical properties of the DETDA-extended
waterborne PUU films were enhanced appreciably; these enhancements are
attributed to the strong hydrogen bonding in urea carbonyl groups and
the ordered structure of hard segments in the systems. The
DETDA-extended PUU film with 40 wt.% of hard segment and 4.0 wt.% of
DMPA unit showed the lowest water-absorbing amount (2.6 wt.%) over all
PUU films studied. The hydrophobic surface of the DETDA-extended PUU
film modified with a small amount of aminoethylaminopropyl
polydimethylsiloxane (AEAPS) was observed and its hydrophobicity was
enhanced by increasing the AEAPS content further.

Recently, for environmental protection the waterborne polyurethane
(PU) and polyurethanurea-acrylate (PUA) have gained greater
attention,(1-3) and are widely used to prepare some coatings, adhesives,
and surface finishes for textiles. These PU and PUA have the advantages
of low volatile compound and excellent mechanical properties. Many works
have been carried out to study the effects of soft segment, hard
segment, neutralizing agent and hydrophilic monomer on the physical
properties of the waterborne PU and PUA, which are often prepared with
ethlenediamine (EDA) as chain extender. (2),(4),(5) Chen et al. (6)
prepared a series of waterborne PUs with L-lysine, EDA, and L-lysine/
EDA mixture as extenders, respectively. It was found that the water
absorption of PU film prepared with the L-lysine was higher than those
of other films, but it showed the smallest hydrolysis weight loss among
the three samples. Yen et al. (7) Studied the mechanical properties of
several waterborne PUs prepared with different diamines or diols as
chain extenders, such as EDA, diethyltriamine, and 1,4-butanediol, and
found that the mechanical properties of the PUs prepared with diamine as
chain extender were better than those prepared with 1,4-butanediol.
Delpech and Coutinho (8) also studied the influence of various chain
extenders on the properties of the waterborne PUs and found that the
EDA-extended PU film exhibited better mechanical propertied than the
hydrazine-extended one.

Diethltoluenediamine (DETDA) has been used as a chain extender in
reaction injection molding of PU system resulting from its low
reactivity, (9) but it has not been used in preparing the waterborne PU
or PUA. In this article, a series of DETDA-extended polyurethaneurea
(PUU) aqueous dispersions with different hard segment contents were
prepared, and the effect of hard segment on the physical properties of
PUU aqueous dispersions and their films was observed. Compared with the
EDA-extended waterborne PUU, the physical properties of the
DETDA-extended PUU aqueous dispersion only slightly changed, but for
this kind of PUU film the mechanical properties were enhanced and the
water-absorbing amount decreased appreciably. Furthermore, the
DETDA-extended PUU aqueous dispersions were modified with
aminoethylaminopropyl polydimethylsioxane (AEAPS), and it was found that
the water resistance of their films was enhanced further.

P756, DMPA, NMP, and IPDI were charged into a 250-ml foru-necked,
round-bottom flask equipped with a mechanical stirrer, an inlet of dry
nitrogen, a condenser, and a thermometer. It was then heated to
80[degrees]C for 3-4 h until the theoretical NCO content was reached,
which was tested with a standard dibutylamine back titration method.
This NCO-terminated prepolymer was neutralized by adding TEA at
50[degrees]C, then it was dispersed into deionized water and
chain-extended at 50[degrees]C using DETDA or EDA as a chain extender to
prepare the PUU aqueous dispersions were prepared at 33wt.% solid
content. For simplicity, the PUUs chain-extended by DETDA and EDA were
called PU-D-X and PU-E-X, respectively, in which X represented the hard
segment content.

Under vigorous stirring, AEAPS emulsion was dispersed into the PUU
aqueous dispersion chain-extended by DETDA to prepare a modified PUU
aqueous dispersion. For simplicity, the modified PUU aqueous dispersion
was called M-Y, in which Y represented the AEAPS content.

PUU films were prepared by casting the aqueous dispersions into a
poly(tetrafluoraethylene) mold under ambient conditions. The films were
dried at ambient temperature for 1 week and then dried to a constant
weight under vacuum at 60[degrees]C.

Measurements

The particle size of the PUU aqueous dispersion was determined by a
Mastersizer 2000 particls size analyzer. The viscosity of the aqueous
dispersion was measured by NDJ--79 rotation viscometer at a shear rate of 2000 [s.sup.-1]. The surface tension of the PUU aqueous dispersion
was tested using the drop volume method. Above measurements were all
performed at 25[degrees]C. The high-temperature stability of the aqueous
dispersion was determined by observing whether the aqueous dispersion
precipitated or not after heating to 60[degrees]C for 40 h in an oven.
For measuring the freeze-thaw stability of the aqueous dispersion, the
PUU aqueous dispersion was cooled to -20[degrees]C for 18 h and kept at
ambient temperature for 6 h. This cycle was repeated five times to
observe whether the aqueous dispersion precipitated or not. FTIR spectra
of the PUU films were measured with a Nicolet 5DXC FTIR spectrometer at
ambient temperature. Differential scanning calorimetry (DSC) was
measured with a TA Instruments 2910 modulated DSC analyzer at a heating
rate of 10[degrees]C [min.sup.-1] under a nitrogen atmosphere. The
mechanical properties for all the specimens were conducted on an Instron
4465 testin machine at a crosshead rate of 50 mm [min.sup.-1], and the
specimens were made in accrodance with GB1040-79. The hardness of PUU
film was tested according to GB/G170393. The contact angle of water on
the surface of the film was measured by using a JC2000A Contact Angle
Measuring Apparatus at ambient temperature.

The water absorption of the PUU film was determined by immersing a
film (20 x 20 x 1 mm) in deionize water at 25[degrees]C for 24 h, then
the sample was blotted dry and weighed. The water absorption was
calculated as follows:

where, [[gamma].sub.s], [[gamma].sub.s.sup.d], and
[[gamma].sub.s.sup.P] are the surface energy, the dispersion component
of the surface energy and the polar component of the surface energy for
PUU film, respectively; [[gamma].sub.1], [[gamma].sub.1.sup.d], and
[[gamma].sub.1.sup.p] are the surface tension, the dispersion component
of the surface tension and the polar component of the surface tension
for water, respectively ([[gamma].sub.1.sup.d] = 51.0 mN [m.sup.-1],
[[gamma].sub.1.sup.p] = 21.8 mN [m.sup.-1]); [[gamma].sub.2],
[[gamma].sub.2.sup.d], and [[gamma].sub.2.sup.p] are the surface
tension, the dispersion component of the surface tension and the polar
component of the surface for ethylene glycol, respectively
([[gamma].sub.2.sup.d] = 19.0 mN [m.sup.-1], [[gamma].sub.2.sup.p] =
29.3 mN [m.sup.-1]).

Results and discussion

PUU aqueous dispersions

In general, [NCO]/[OH] (molar ratio) calculated mainly from the
isocyanate and polyol in the initial system has great effect on the
structure morphology, and property of PU synthesized. Xu et al. (11)
found that the PUA aqueous dispersion tended to gel if the [NCO]/[OH]
was less than 1.3, and the aqueous dispersion was not stable with wide
particle size distribution, if the [NCO]/[OH] was more than 2.0. Thus,
for preparing waterborne PUU it is appropriate to control the [NCO]/[OH]
from 1.3 to 2.0. A series of PUU aqueous dispersions with different hard
segment structures and contents were prepared by adjusting the DMPA
content and the value of [NCO]/[OH] from 1.3 to 2.0, as shown in Table
1. In order to prepare the PUU aqueous dispersions with different hard
segment contents but at a constant DMPA content, the value of [NCO]/[OH]
was varied accordingly. To keep a 4.0 wt.% concentration of DMPA in PUU,
the hard segment content could be varied within a narrow range, and the
highest hard segment content for PU-D or PU-E system was only at 40% or
35%. In this case, to increase the hard segment content in PUU aqueous
dispersion, the DMPA concentration should also increase, as [NCO]/[OH]
keeps 2.0. Table 1 shows that all the physical properties,. i.e., the
particle size, polydispersity index, viscosity, and surface tension, for
PU-D aqueous dispersions are similar to and/or even better than those
for PU-E aqueous dispersions. This means that the PU-D aqueous
dispersions were successfully prepared with DETDA as chain extender. It
was also found that within the experimental conditions the physical
properties, except the viscosity, only slightly changed for both PU-D
and PU-E aqueous dispersions, although a great difference between the
hard segment (HS) contents as well as the DMPA contents for both systems
was set up. It should be pointed out that this experimental behavior
could be further attributed to a broad tolerance of experimental
conditions for preparing the waterborne PU-D with DETDA as chain
extender.

Table 1 shows that the surface tension of both aqueous dispersion
systems (PU-D and PU-E) decreases with increasing the HS content, and is
independent of the DMPA concentration. This behavior can be attributed
to the microphase separation between the hard and soft segments. The
microphase separation degree or PUU should increase with increasing the
HS content in the system (see the following part), and the surface of
the aqueous dispersion could be occupied by more hydrophobic soft
segment resulting in the lowering of the surface tension. The particle
size for both kinds of PUU aqueous dispersions does not change obviously
and the particle size distribution nearly remains constant with
increasing the HS content and the DMPA concentration, as listed in Table
1. IN this case, the microphase separation morphologies of these
particles seemed to have no significant effect on the particle size. The
hydrophilic DMPA salt unit (for simplicity, it is called DMPA unit)
easily migrates to the surface of the particles during the formation
process of the aqueous dispersions resulting in similar particle size.

The viscosities for both PU-D and PU-E aqueous dispersions are
complicated, as shown in Table 1, but they may be attributed to the
rigidity and the surface charge density of the particles, and should be
studied further. However, the viscosity of PU-D system is lower than
that of PU-E system with similar hard segment content. This experimental
result is of benefit for PU-D to further prepare the line chemical
products, such as adhesives and coatings.

For enhancing the water resistance of waterborne PUU farther, the
DETDA-extended PUU aqueous dispersions were modified with AEAPS and
their physical properties are listed in Table 2. Compared with the
unmodified dispersions, the particle size and the viscosity of
AEAPS-modified PUU aqueous dispersions increase, and the particle size
distribution is still quite narrow, indicating that most of the
hydrophobic AEAPS particles may be wrapped by the PUU macromolecular chains in the systems. (12) The surface tension of the modified PUU
aqueous dispersions is much higher than that of AEAPS emulsion (26.3 mN
[m.sup.-1]) and decreases gradually with the increase of AEAPS content.
When the AEAPS content increases from 5.0% to 7.0%, the surface tension
levels off. Thus, the surface of the dispersed particles in M-7 system
may be saturated with the emulsifying agents present in the original
AEAPS emulsion giving rise to the low surface tension. This behavior may
further confirm that most of the hydrophobic AEAPS particles were
wrapped by the PUU macromolecular chains. The viscosity of the modified
PUU aqueous dispersions increases with increasing the particle size
which may also result from the emulsifying agents existing on the
surface of the particles.

Tables 1 and 2 show that all the PUU aqueous dispersions are very
stable at ambient temperature and they do not precipitate after low- and
high-temperature stability tests. This phenomenon is obviously
significant for further application of these aqueous dispersions in
industry.

PUU films

Table 3 shows that for both kinds of PUU films with 4.0 wt.%
concentration of DMPA the water-absorbing amount decreases remarkably
with increasing the HS content, but the contact angle only increases
slightly. When the HS content in either PU-D or PU-E system is higher
than 40% or 35%, the DMPA concentration in these specimens increases
with increasing the HS content, giving rise to increase the
water-absorbing amount and decrease the contact angle. However, it
should be pointed out that in all cases the water-absorbing amount of
PU-D films is much lower than that of PU-E films and the PU-D-40 him
shows the lowest water-absorption behavior (2.6 wt.%) and the highest
contact angle of water over all specimens studied here. In other words,
this sample exhibits the excellent waterproof performance.

It is well known that PUU is a typical multi-block copolymer consisting of alternating soft and hard segments along the
macromolecular chain. Thus, the strong hydrogen bonding should be formed
not only between the hard segments but also between the soft and hard
segments in the copolymer. The hydrogen bonding directly affects the
ordered structure of hard segments in PUU (3) and was measured by using
FTIR spectrometer, as shown in Fig. 1. The N-H stretching region in FTIR
spectra is too complicated to be analyzed for both PU-D and PU-E films,
so that earlyzed for both PU-D and PU-E films, so the carbonyl stretching region was chosen for investigation. The multiple absorption
bands are observed in the carbonyl region in Fig. 1, which imply
different kinds of hydrogen bonding for urethane carbonyl and urea
carbonyl groups. Thus, the hydrogen bonding between the urea linkages in
PUU was observed, as the absorption peaks for urethane groups would be
affected by the carbonyl absorption peaks of polyester soft segment. It
should be pointed out that the carbonyl absorption peak of DMPA units
present in the PUU macromolecular chains is located at 1550 [cm.sup.-1],
which would not influence the study of hydrogen bonding for urea groups.
(3) The iteration procedure of damping least squares was used to
separate the absorption peaks in the carbonyl region (13) (Fig. 1)
corresponding to different hydrogen bondings (see Table 4), and the
curvefitting results are shown Fig. 2 and Table 5. The degree of
hydrogen bonding for urea groups ([X.sub.b,UA]), the percentage of
ordered urea-urea hydrogen bonds ([X.sub.o,UA]), and the percentage of
disordered urea-urea hydrogen bonds ([X.sub.d.UA]) in Table 5 were
defined as follows:

Table 5 shows that both the hydrogen bonding degree of urea groups
([X.sub.b,UA]) AND THE VALUE OF [x.sub.o,UA] for PU-D systems are higher
than those of PU-E systems containing nearly the same HS content.
Furthermore, the value of [X.sub.b,UA] for both kinds of PUU films
increases with increasing the HS content. It is clear that the PU-D
films should have better ordered structure of hard segments than the
PU-E films, which is beneficial for protecting the hydrophilic DMPA
unit, so as to decrease the amount of water absorption of the film. It
is of interest to note that the surfaces of these films are not affected
by the ordered structure of the hard segments appreciably, so that the
values of the water contact angle measured and the surface energy
estimated only slightly change. While the HS content in either PU-D or
PU-E system is higher than 40% or 34%, the values of [X.sub.b,UA] and
[X.sub.o,UA] increase a bit with increasing the HS content, because the
DMPA units in HS interfere with the formation of the hydrogen bonding.
Thus, the water-resistance ability for both kinds of PUU films decreases
when the HS content in PU-D or PU-E film is higher than 40% or 35%,
mainly because the hydrophilicity of PUU films increase with increasing
the concentration of hydrophilic DMPA unit.

Figure 3 shows the DSC scan curves for DETDA-extended PUU films
with different HS contents, and the DSC scan results are listed in Table
6. Table 6 shows that the glass transition temperatures ([T.sub.gs]) of
the PUU films shift to high temperature, as compared with that of
polyester polyol used. It indicates some compatibility between the soft
segment and the hard segment in these PUU films. A small endothermic peak was observed in Fig. 3 at 134[degree]C or 150[degree]C ([T.sub.a])
for PU-D-34 or PU-D-40 specimen, which should be attributed to the
disruption of some domains and/or crystallites composed of the ordered
hard segments. (14) There is no endothermic peak for the PU-D-28 film
with low HS content and low value of [X.sub.b,UA]. These experimental
data further confirm that the ordered structure of hard segments is
enhanced with increasing the HS content, and coincide with the FTIR
observation.

Table 7 lists the surface properties and the water-absorbing
amounts of the DETDA-extended PUU films modified with AEAPS. For these
modifies samples, the contact angle increases and the [[gamma].sub.s]
decreases with increasing the AEAPS content. The surface of modified PUU
film shows the hydrophobic capacity when the AEAPS content is more than
1 wt.%. This means that the hydrophobic AEAPS units may enrich on the
surface of the modified PUU film during the film formation process. (12)
The water-absorbing amount of these modified PUU films only increasing a
little, which may be also attributed to the emulsifying agent existed in
the AEAPS emulsion, as discussed before.

The mechanical properties for different PUU films were measured, as
listed in Tables 8 and 9. Table 8 shows that the introduction of the
rigid phenyl ring from DETDA in the PUU macromolecular chain gives rise
to increase the hardness and tensile strength for PU-D films compared to
those for PU-E films. For both kinds of PUU films, the hardness and the
tensile strength increase and the elongation at break decreases with
increasing the HS content. Table 9 shows that the hardness and tensile
strength of AEAPS-modified PUU films decrease due to the introduction of
flexible AEAPS units in the systems.

In conclusion, a series of PUU aqueous dispersions with DETDA as
chain extender were prepared and characterized. The experimental results
showed that these PUU aqueous dispersions had excellent freeze-thaw and
high-temperature stability, and exhibited similar particle size and
surface tension, but low viscosity, compared to those prepared with EDA
as chain extender. The particle size of AEAPS-modified PUU aqueous
dispersions increases compared with the unmodified one. The water
resistance and the mechanical properties of the DETDA-extended PUU films
were enhanced appreciably. The DETDA-extended PUU film with 40 wt.% of
HS and 4.0 wt.% of DMPA unit showed the lowest water-absorbing amount
(2.6 wt.%) over all PUU films studied. The hydrophobicity of the
DETDA-extended PUU films modified with AEAPS was enhanced further.